Metal/carbide-oxide composite

ABSTRACT

DISCLOSED ARE COMPOSITE STRUCTURES COMPRISING (1) A DENSE, METAL-BONDED REFRACTORY CARBIDE-OXIDE ELEMENT METALLURGICALLY BONDED WITH A COPPER-ALLOY TO(2) A DENSE, COBALT-BONDED TUNGSTEN CARBIDE ELEMENT HAVING A SUBSTANTIALLY UNIFORM COEFFICIENT OF THERMAL EXPANSION OF FROM 0.5 TO 1.5 TIMES THAT OF SAID CARBIDE-OXIDE ELEMENT. THE COMPOSITES ARE PARTICULARLY USEFUL AS CUTTING EDGES FOR MILLING AND TURNING CASTIRON AND HARDENED STEELS.

July l1, 1972 D, M CHAY EI'AL 3,676,086

METAL/CARBIDE-OXIDE COMPOSITE Original Filed Nov. 25, 1968 /L TUNGSTENCARBIDE e-METAL BoNol-:D REFRAcToRY f cARBaDE-OXIDE 3,676,086 METAL/CARBIDE-OXIDE COMPOSITE Dong M. Chay and Ralph K. Iler, Wilmington,Del., assignors to E. I. du Pont de Nemours and Company, Wilmington,Del.

Original application Nov. 25, 1968, Ser. No. 784,999, now Patent No.3,567,408, dated Mar. 2, 1971. Divided and this application Dec. 8,1970, Ser. No. 96,292

Int. Cl. B32b 15/00 U.S. Cl. 29-195 12 Claims ABSTRACT OF THE DISCLOSUREDisclosed are composite structures comprising (l) a dense, metal-bondedrefractory carbide-oxidel element metallurgically bonded with acopper-alloy to (2) a dense, cobalt-bonded tungsten carbide elementhaving a substantially uniform coeicient of thermal expansion of from0.5 to 1.5 times that of said carbide-oxide element. The composites areparticularly useful as cutting edges for milling and turning cast ironand hardened steels.

CROSS-REFERENCE TO RELATED APPLICATION This application is a division ofapplication Ser. No. 784,999, led Nov. 25, 1968, now Pat. 3,567,408.

DESCRIPTION OF T HE INVENTION General The metallurgical bond connectingthe carbide-oxide and the metal to the cobalt-bonded tungsten carbidecomprises a copper-alloy with a highly reactive metal such as titanium,zirconium, or hafnium.

This invention is directed to a composite structure comprising (1) adense, metal-bonded refractory carbideoxide element, (2) a metalsupporting element and (3) a dense, cobalt-bonded tungsten carbideelement metallurgically bonded between the carbide-oxide element and thesupporting element, the tungsten carbide element having a substantiallyuniform coeicient of thermal expansion of from about 0.5 to about 1.5times that of the carbide-oxide body.

This invention is further directed to a method of securing a dense,metal-bonded refractory carbide-oxide element to a metal supportcomprising metallurgically bonding the carbide-oxide element with acopper alloy to a dense, cobalt-bonded tungsten carbide base having asubstantially uniform coeicient of thermal expansion of from about 0.5to about 1.5 times that of said carbideoxide-element and thereaftermetallurgically bonding the tungsten carbide base to the metal support.

The composite structures are useful tools for milling and turning castiron and hardened steels, and as equipment parts with wear resistant,corrosion resistant, and temperature resistant facings.

It is difficult to join the dense carbide-oxides and metal supports,such as steel tool shan'ks, for two reasons.

First, the surface of carbide-oxide tends to be oxidized during theprocess of brazing in air. If the carbide portion of the surface doesbecome oxidized, the surface is difficult to wet with conventionalbrazes and solders.

The second, and more troublesome, problem encountered when attempting tobond the dense carbide-oxide composites directly to metals such as steelis caused by the difference between the coeiiicientspf thermal expansionof the two materials. The metal contracts much more than the densecarbide-oxide composite as the two cool after being metallurgicallybonded, causing the laminate to bend with the outer surface of thecarbide-oxide being subjected to such`a strain that it cracks. In anattempt to overcome the thermal mismatch problem, shims of copper andbronze have been used between the dense carbide-oxide and metal; butmuch of the strain is still transmitted to the dense carbide-oxide.

'One technique which has been suggested for securing materials ofmarkedly different expansion coefficients involves the use of aconnecting element commonly referred to as a graded seal. This type ofconnecting element has an expansion coefficient which varies along itslength in a stepwise or continuous manner and at each end matches thatof the material to which it is bonded. In Zimmer, U.S. Pat. No.3,284,174 and in Zimmer, 'New Ways to Bond Dissimilar Materials,Material Progress (TM), January 1963, the use of graded seals producedby powder metallurgy is'discussed in detail.

While the use of graded seals usually makes it possible to obtain verysecure bonds between dissimilar materials, it also has some unattractiveaspects. For example, the production of graded seals is ordinarily verytedious and costly, and the seals often require more space than isavailable in many applications for dense carbide-oxides. Also, theexpansion coeicients of both of the materials to be joined must be knownbefore the seals can be produced.

It has been found that metal-bonded refractory carbideoxide compositescan be secured to a metal such as steel Without using connectingelements of continuously varying compositions. More particularly, it hasbeen discovered that this can be accomplished by using a dense,cobalt-bonded tungsten carbide connecting element having a high cobaltcontent and thus a substantially uniform expansion coefficientapproximating that of the carbideoxide.

For simplicity, the dense, metal-bonded refractory carbide-oxidecomposites used in the methods and structures of this invention arehereinafter referred to merely as carbide-oxide elements or ascarbide-oxide cutting edges; likewise, the dense, cobalt-bonded tungstencarbide composites are referred to as tungsten carbide bases." Compositestructures in which a carbide-oxide element is metallurgically bonded toa tungsten carbide base are termed laminates The metallurgical bond ofthe copper alloy is termed the bond.

The drawing FIG. 1 represents a cross-section of a tool for milling andturning hard materials such as alloy steels. A dense metal-bondedrefractory carbide-oxide cutting edge 1 is bonded to a slice of dense,tungsten carbide base 2 by means of a layer of braze 3 which ispreferably a coppertitanium alloy. The tungsten carbide base, which hasan expansion coeicient of from about 0.5 to about 1.5 times that of thecutting edge, s bonded to a steel shank 4 through a low-melting silversolder 5.

FIG. 2 represents a cross-section of an indexable insert for a cuttingtool wherein a carbide-oxide cutting edge 6 is bonded to a tungstencarbide base 7 through preferably a copper-titanium alloy brazingmaterial 8, the base having an expansion coefficient approximating that0f the cutting edge. Inserts such as the one in FIG. 2 can be secured toa cutting tool (not shown) by brazing the base to the tool, for exampleby using a low-melting silver solder and a hand torch.

Carbide-oxide elements The refractory carbide-oxide which comprises thecarbide-oxide elements used in the methods and structures of thisinvention are those described in copending application Ser. N'o.737,223, filed June 14, 1968 by Bergna et al. entitled Metal BondedAlumina-Carbide Compositions, the disclosure of which is incorporatedherein by reference. That application discloses carbide-oxide densecompositions having an average grain size smaller than 10 microns andcomposed of two interpenetrating three-dimensional networks, one networkof alumina and the other network of metal and a carbide selected fromthe group consisting of zirconium carbide, hafnium carbide, titaniumcarbide and their mixtures, the composition consisting essentially of 20to 90 volume percent alumina, 5 to 79 volume percent carbide and 1 to 20volume percent metal, said metal consisting essentially of 5 to 90weight percent of a metal selected from the group consisting of iron,cobalt, nickel and their mixtures and to 95 weight percent of a metalselected from the group consisting of tungsten, molybdenum and theirmixtures, with the limitation that the volume percent of carbide mustnot be less than that of the metal.

Of the carbide-oxide bodies disclosed in Ser. No. 737,- 223, those whichare preferred for use in the methods and structures of this inventionare those compositions having an average grain size smaller than 5microns and composed of two interpenetrating three-dimensional networks,one network of alumina and the other network of metal and titaniumcarbide, the composition consisting essentially of 40 to 75 volumepercent alumina, 12.6 to 58 volume percent titanium carbide, and 2 to 20volume percent metal, wherein said metal consists essentially of 5 to 90weight percent nickel and 10 to 95 Weight percent molybdenum, with thelimitation that the volume percent of carbide must not be less than thatof the metal.

Particularly strong bonds are obtained between the carbide-oxide elementand tungsten carbide base if the former is an electrical conductor andhas a specic resistivity of less than 3000 microhm-centimeters.Ordinarily, carbide-oxide elements containing less than 30 volumepercent of electrically conducting phases of carbide and metal will havespecific resistivities of greater than 3000 microhm-centimeters, whereasthose containing more than 30% of an electrically conducting phases willhave specilic resistivities of less than 3000 microhal-centimeters. Atsome value between 20 and 30 volume percent the specic resistivity for agiven combination of components changes very markedly as the amount ofelectrically conducting phase is varied slightly. The exact value atwhich the specific resistivity changes at a maximum rate depends to agreat extent on distribution of the electrically conducting phase. Thestrongest bonds are obtained with carbide-oxide elements having specilicresistivities of less than 500 microhm-centimeters.

Tungsten carbide bases The bases used in this invention to secure thecarbideoxide elements to steel supports are comprise of cobalt bondedtungsten carbide, i.e., nely divided tungsten carbide bonded with ametallic phase of cobalt. As pointed out above, these bases havesubstantially uniform expansion coefficients of from about 0.5 to about1.5 times that of the carbide-oxide. Preferably the expansioncoefficient will be from about 0.8 to about 1.0 times that of thecarbide-oxide. Thus, if the carbide-oxide element has a coeflicient ofexpansion of 8)(10-6/D C., the base will preferably have a coeicient ofexpansion of at least less about 6.4 106/ C.

The expansion coefficient of cobalt-bonded tungsten carbide is primarilydependent on its cobalt concentration. According to Russian Metallurgyand Mining Journal 1964, No. l, pages 113 to 121, cobalt-bonded tungstencarbides containing 6%, 10% and 12% by weight of cobalt has coeicientsof thermal expansion of 5.0X10-6, 5.3 106 and 6.3 X 106 per degreecentigrade, respectively. If 25% cobalt is present, the coeicient is6.4X 10-6/ C. or higher. Since dense, metal-bonded refractorycarbide-oxides ordinarily have expansion coeicients ranging from 6x106to 8.5 10G per degree centigrade, cobaltbonded tungsten carbidecompositions containing more than 12% cobalt with suitably matchingexpansion coefficients can be produced.

Tungsten carbide bases having densities of at least 99% of theoreticalare generally preferred for use in this invention because of their highstrength and stiiness.

Metallurgical bonding A variety of metallurgical bonding techniques canbe used to produce the structures of this invention, but care must betaken to avoid oxidation of the freshly cut surface of the carbide-oxidebody. The metallurgical bond can be formed for example by hot pressingthe elements to one another, but brazing techniques are preferred.

Brazing metals suitable for bonding are strong, ductile metals havingmelting points higher than about 1000o C., e.g., copper. Although copperalone often will not bond well to the carbide-oxide material, a copperalloy containing less than 50% titanium, zirconium, or hafnium is veryeicient.

In one preferred method of forming the metallurgical bond a freshly cutcarbide-oxide element is sand-blasted to remove all traces of dust orgrease. A sheet of titanium foil about 0.1002 inch. in thickness isplaced on this surface and over this is placed a cleaned, pure copperfoil from 0.005 to 0.015 inch thick after which the tungstencarbide baseis placed against the copper. The resulting sandwich is bound togethertightly with Nichrome or pure iron wire. This assembly is thenpositioned in a high vacuum furnace so that the foils are situatedhorizontally and is heated to about 1500 C. for 5 minutes under a vacuumat a pressure of less than 10-4 torr. The heating need only be longenough to establish good wetting of the surfaces by the resulting liquidcopper alloy. The assembly is allowed to cool to about 200 C. in lessthan about ten minutes and is removed from the furnace. The carbide sideof the resulting laminate is cleaned by sandblasting and is brazed to ametal support using a conventional low-melting silver solder.

While a copper-titanium alloy made from metal foils or sheets asdescribed above is one of the preferred brazing materials for joiningthe carbide-oxide element to the tungsten carbide base, it is alsopossible to use preformed high-copper alloys of copper containingtitanium, zirconium, or hafnium to improve the bonding to thecarbideoxide.

Brazing of the carbide-oxide element and tungsten carbide base carriedont in the absence of reactive gases such as oxygen or nitrogen. Anargon or helium atrnosphere may be used but a high vacuum is preferred.

For joining the tungsten carbide bases to steel, lowmeltingsilver-containing solders ordinarily used to secure cobalt-bondedtungsten carbide cutting edges to steel can be employed. A preferredsolder for this purpose is a silver solder designated B-Ag3, ASTMClassification, which has a solidus Itemperature of 1170 F and consistsof 50% silver, 15.5% copper, 15.5 zinc, 16% cadmium and 3% nickel.

Cutting tools of this invention, utilizing the carbideoxide element asthe cutting edge, include reamers, grooving tool, milling blades, formtools, gun drills, and turning tools used on tracer lathes. The highwear resistance of the cutting edge and the strength and toughness ofthe cobalt-bonded carbide base provide long-lasting tools of particularvalue in automatically controlled metal-shaping machines.

The following examples are illustrative of the subject matter of thisinvention.

EXAMPLE 1 Carbide-oxide composition The carbide-oxide compositioncontains 50% by volume aluminum oxide, 45% by volume of titaniumcarbide, and 21/2% by volume each of nickel and molybdenum and has beenhot pressed at 1800 C. for 7 minutes at 4,0!00 p.s.i. The carbide-oxidehas the following properties:

Expansion coefficient: 8 X 10-6/ C., Specific resistivity: 400microhm-centimeters, Density: 99}-% of theoretical, and Dimensions: 1inch x 1 inch x j/16 inch.

Tungsten carbide composition Composition: 75% by Weight of tungstencarbide and 25% by weight of cobalt,

Expansion coefcient: 7X 10-6/ C.,

Density: 99-}-% of theoretical, and

Dimensions: l inch x 1 inch x 3/16 inch.

The carbide-oxide and tungsten carbide slices are each ground at on oneside to a surface iinish of 100 microinches and are then cleaned andgiven a matte finish by sand-blasting. A sheet of titanium foil 0.002inch thick and a sheet of copper foil 0.010 inch thick is placed betweenthe surfaces, the titanium being next to the carbideoxide. The assemblyis then tied together tightly with a No. 24 Nichrome wire and is heatedto 1200 C. in ten minutes under a vacuum of 104 torr. This temperatureis maintained for ve minutes and the assembly is then cooled to lessthan 600 C. within 15 minutes and then further to 200 C. before removingthe laminate from the vacuum.

The carbide side of the laminate is then brazed to a steel cutting toolshank in a conventional manner with silver solder having a melting pointbelow 900 C. The tool is then diamond ground and used for turninghardened AISI 4340 alloy steel having a hardness on the Rockwell C scaleof 55, at 800 surface feet per minute, a feed of 0.010 inch perrevolution and a depth of 0.050 inch.

EXAMPLE 2 Three laminates 11A@ inches by 11/16 inches square and 1A inchthick are produced as described in Example 1. Each laminate is diamondsawed into four equal square pieces which are finished ground to formrectangular cutting inserts (0.500 by 0.500 by inch) having a radium of1/32 inch ground on each corner. The twelve inserts so produced arebrazed in a negative rake milling head which is then used to face millgray cast iron castings at 1200 surface feet per minute, 0.010 inch feedper tooth, 0.050 inch depth and two inches width of cut. A total cut of1000 feet in length is made before the inserts fail and need to bereground.

We claim:

1. A composite structure comprising l) a dense, metalbonded refractorycarbide-oxide elment, (2,) a metal supporting element, and (3) a dense,cobalt-bonded tungsten carbide element metallurgically bonded betweenthe carbide-oxide element and the metal supporting element, the tungstencarbide element having a substantially uniform coeicient of thermalexpansion of from about 0.5 to about 1.5 times that of saidcarbide-oxide element.

2. The composite structure of claim 1 wherein said tungsten carbideelement has a substantially uniform expansion coeicient of from about0.8 to about 1.0 times that of said carbide-oxide element.

3. The composite structure of claim 1, wherein said carbide-oxideelement has a specific resistivity of less than 3000microhm-centimeters.

4. The composite of claim 3 wherein said carbideoxide element has aspecic resistivity of less than 500 microhm-centimeters.

5. A composite structure comprising (1) a metalbonded refractorycarbide-oxide element consisting essentially of a dense compositionhaving an average grain size smaller than 10 microns and composed of twointerpenetrating three-dimensional networks, one network of alumina andthe other network of metal and a carbide selected from the groupconsisting of zirconium carbide, hafnium carbide, titanium carbide, andtheir mixtures, said composition consisting essentially of 20 to 90volume percent alumina, 5 to 79 volume percent carbide, and 1 to 2.0volume percent of a metal, said metal consisting essentially of 5 to 90yweight percent of a metal selected from the group consisting of iron,cobalt, nickel, and their mixtures, and 10 to 95 weight percent of ametal selected from the group consisting of tungsten, molybdenum, andtheir mixtures, with the limitation that the volume percent of carbidemust not be less than that of the metal; (2) a steel supporting element;and (3) a cobalt-bonded tungsten carbide element having a density of atleast 98% of theoretical and a substantially uniform coecient of thermalexpansion of from about 0.5 to about 1.5 times that of saidcarbide-oxide element; the tungsten carbide element beingmetallurgically bonded between the carbide-oxide element and the metalsupporting element, and the metallurgical bond between the carbide-oxideelement and the tungsten carbide element being a copper-rich alloy witha material selected from the group consisting of titanium, zirconium,and hafnium.

6. The composite structure of claim 5 wherein said carbide-oxide elementis in the form of a cutting edge.

7. The composite structure of claim 5 in which the alumina is present insaid carbide-oxide element in an amount ranging from 40- to 75 volumepercent.

8. The composite structure of claim 5 in which said carbide-oxideelement consists essentially of 40 to 75 volume percent of alumina,`12.6 to 58 volume percent of carbide, and 2 to 20 volume percent ofmetal.

9. The composite structure of claim 8 in which said carbide-oxideelement consists essentially of about 50 volume percent alumina, about45 volume percent titanium carbide, about 2.5 volume percent nickel, andabout 2.5 volume percent molybdenum.

10. The composite structure of claim 5 wherein the carbide of saidcarbide-oxide element is titanium carbide.

1K1. The composite structure of claim 5 wherein the metal of saidcarbide-oxide consists essentially of nickel and molybdenum.

12. The composite structure of claim 5 wherein said canbide-oxideelement has an average grain size smaller than 5 microns.

References Cited UNITED STATES PATENTS 2,886,885 6/1958 Macdonald et al.29-47'29 2,963,782 12/ 1960 Donnelly 29-195 X 3,139,329 6/1964 Zeller29-195 3,552,939 1/ 1971 Darnell et al. 29--195 L. DEWAYNE RUTLEDGE,Primary Examiner E. L. WEISE, Assistant Examiner

